A Simple Low-Temperature Glass Bonding Process with Surface Activation by Oxygen Plasma for Micro/Nanofluidic Devices

Abstract

The bonding of glass substrates is necessary when constructing micro/nanofluidic devices for sealing micro- and nanochannels. Recently, a low-temperature glass bonding method utilizing surface activation with plasma was developed to realize micro/nanofluidic devices for various applications, but it still has issues for general use. Here, we propose a simple process of low-temperature glass bonding utilizing typical facilities available in clean rooms and applied it to the fabrication of micro/nanofluidic devices made of different glasses. In the process, the substrate surface was activated with oxygen plasma, and the glass substrates were placed in contact in a class ISO 5 clean room. The pre-bonded substrates were heated for annealing. We found an optimal concentration of oxygen plasma and achieved a bonding energy of 0.33–0.48 J/m2 in fused-silica/fused-silica glass bonding. The process was applied to the bonding of fused-silica glass and borosilicate glass, which is generally used in optical microscopy, and revealed higher bonding energy than fused-silica/fused-silica glass bonding. An annealing temperature lower than 200 °C was necessary to avoid crack generation by thermal stress due to the different thermal properties of the glasses. A fabricated micro/nanofluidic device exhibited a pressure resistance higher than 600 kPa. This work will contribute to the advancement of micro/nanofluidics.

Microfluidic technology and its application in the point-of-care testing field

“…Common direct bonding methods include thermal bonding ( Abgrall et al, 2007 ; Wang et al, 2011 ; Yin et al, 2018 ), surface modification bonding ( Bhattacharyya and Klapperich, 2007 ; Zhou et al, 2010 , 2012 ), and ultrasonic bonding ( Zhang et al, 2010b ), and indirect bonding techniques include solvent bonding ( Brown et al, 2006 ; Gan et al, 2011 ; Hsu and Chen, 2007 ; Koesdjojo et al, 2008 ; Sun et al, 2007 ) and adhesive bonding ( Thompson and Abate, 2013 ; Wu et al, 2005 ). According to the different chip materials, the bonding methods of silicon and glass chips include thermal bonding ( Abgrall et al, 2007 ; Xu et al, 2012 ), anode bonding ( Xu et al, 2012 ), and low temperature bonding ( Bart et al, 2009 ; Shoda et al, 2020 ), while the bonding methods of polymer microfluidic chips include thermal bonding ( Hu et al, 2016 ; Wang et al, 2011 ; Yin et al, 2018 ), solvent bonding ( Brown et al, 2006 ; Gan et al, 2011 ; Hsu and Chen, 2007 ; Koesdjojo et al, 2008 ; Song and Park, 2017 ; Sun et al, 2007 ), adhesive bonding ( Thompson and Abate, 2013 ; Wu et al, 2005 ), plasma bonding, and UV irradiation bonding ( Bhattacharyya and Klapperich, 2007 ; Hui et al, 2005 ; Tsao et al, 2007 ; Wu et al, 2005 ; Yin et al, 2015 ). Thermal bonding is the most common method of bonding.…”

Super-Resolution Defocusing Nanoparticle Image Velocimetry Utilizing Spherical Aberration for Nanochannel Flows

“…To construct the device, the fused-silica substrate was bonded with the borosilicate glass substrate using a lowtemperature bonding method that prevents glass breaking due to the different thermal expansion coefficients of fused-silica glass and borosilicate glass. 43 The substrates were washed in a mixed solution of sulfuric acid and hydrogen peroxide (3:1). After irradiating the oxygen plasma onto the substrates for 40 s, the substrates were made to contact and heated at 110 °C for 2 h.…”

A simple and reversible glass–glass bonding method to construct a microfluidic device and its application for cell recovery

“…Such issues can be barriers to entry in this field and should be addressed to promote wide use of glass microfluidic devices. Other glass bonding techniques performed at low temperature have also been reported including the methods using two-step plasma treatment (O 2 etching plasma irradiation followed by a nitrogen microwave radical activation), 36 O 2 /CF 4 plasma irradiation, 37 vacuum ultraviolet (VUV) light irradiation, 38 irradiation only by O 2 plasma, 39 treatment with hydrogen fluoride steam 40 or hydrofluoric acid, 41 pulse laser irradiation, 42 or an intermediate gluing layer. 43 Recently, glass bonding techniques for reuse have also been reported the methods with O 2 plasma irradiation and heating at 110 °C (ref.…”